<!DOCTYPE HTML>
<html>
<head>
<meta charset="utf-8">
<title>无标题文档</title>
<style>
#div1 {width:200px; height:200px; background:red; position:absolute; left:200px; top:150px; margin:50px;}
</style>
</head>

<body>
<div id="div1" onclick="alert(this.offsetLeft);">
</div>
</body>
</html>
